The present invention relates to a method and apparatus for displaying charge levels of a battery and, more particularly, to a method and apparatus for displaying charge levels of a battery which is connected to an electronic device to power operation of the electronic device.
There are many previously known designs for apparatus which display charge levels of a battery. For example, U.S. Pat. No. 5,130,659 describes a battery monitor which indicates the projected time until a battery reaches a lower threshold value indicative of the energy capacity of the battery. The battery monitor includes a microprocessor which iteratively reads the value of the battery voltage. The microprocessor then determines the rate of discharge of the battery and projects the future values of the battery voltage as well as the projected time at which the battery voltage attains the threshold voltage. This projected time is then displayed on a visual indicator, such as an LCD display. U.S. Pat. No. 5,043,651 discloses an apparatus having a rechargeable battery and a battery voltage detector which detects the output voltage of the battery to produce a detection signal when the output voltage falls below a predetermined threshold level. A controller stores a battery capacity value and accumulates the discharge of the battery to produce an accumulated capacity value. The controller also calculates a difference between the stored capacity value and the accumulated capacity value. Using the difference, a display displays the remaining charge value of the battery thereon. If the difference exceeds a predetermined value at a time the controller receives the detection signal, the controller changes the stored capacity value to a new capacity value. In addition, U.S. Pat. Nos. 3,940,679; 4,755,733; 4,827,220; 5,027,294; 5,105,180; 5,107,196; 5,124,627; 5,130,658; and 5,159,258 relate to other devices for displaying indicia of characteristics of a battery.
However, when a battery is connected to an electronic device, such as a portable computer, to power operation of the electronic device, it may sometimes be desirable to quickly acquire knowledge of the charge level of the battery during a period of non-use of the electronic device. This is true since batteries which power electronic devices, such as a portable computers, include Nickel Cadmium type batteries and Nickel Metal Hydride type batteries. These battery types have an inherent self-discharge characteristic whereby if the battery is left uncharged for a substantial amount of time (e.g. several days), it will lose a significant portion of its charge without the electronic device ever being turned "on". As a result, it is advantageous for a user to acquire knowledge of the charge level of the battery prior to using the electronic device after a period of non-use in order to determine if a recharge is imminently needed. However, in order to acquire knowledge of the charge level of the electronic device, the user will have to go through the process of turning "on" the electronic device and then viewing the charge level indicator in order to acquire knowledge of the charge level. This process may be very time consuming especially in electronic devices, such as portable computers, which must undergo an initial boot cycle each time the device is turned "on". Moreover, in the case where a portable computer is transported from stowed location to a remote site after a period of non-use, the only purpose for initially turning the device "on" and waiting for completion of the boot cycle at the stowed location would be to acquire knowledge of the existing charge level of the battery in order to determine if the battery is sufficiently charged to power operation of the portable computer at the remote location for a desired amount of time.